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libmc-nbt/build.gradle.kts

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+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+kotlin {
+    explicitApi()
+    withSourcesJar()
+
+    linuxX64()
+    linuxArm64()
+    macosArm64()
+    mingwX64()
+    iosArm64()
+    iosSimulatorArm64()
+    jvm { compilerOptions.jvmTarget = JvmTarget.JVM_1_8 }
+
+    sourceSets {
+        commonMain.dependencies {
+            implementation(project(":common"))
+        }
+
+        jvmMain.dependencies {
+
+        }
+
+        commonTest.dependencies {
+            implementation(kotlin("test"))
+            implementation(libs.kotlinx.coroutines.test)
+        }
+    }
+}

libmc-nbt/src/commonMain/kotlin/cn/rtast/libmc/nbt/nbt_reader.kt

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+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/4
+ */
+
+
+package cn.rtast.libmc.nbt
+
+import cn.rtast.libmc.common._Buffer
+import cn.rtast.libmc.common.readVarInt
+
+public class NbtReader(
+    private val buffer: _Buffer,
+    private val variant: NbtVariant = NbtVariant.JAVA,
+) {
+    private fun readShort(): Short = buffer.readShort(variant.order)
+    private fun readInt(): Int = buffer.readInt(variant.order)
+    private fun readLong(): Long = buffer.readLong(variant.order)
+    private fun readFloat(): Float = Float.fromBits(readInt())
+    private fun readDouble(): Double = Double.fromBits(readLong())
+
+    private fun readString(): String {
+        val length = if (variant.isNetwork) buffer.readVarInt() else readShort().toInt() and 0xFFFF
+        if (length == 0) return ""
+        return buffer.readBytes(length).decodeToString()
+    }
+
+    private fun readTagType(): Byte = if (variant.isNetwork) buffer.readVarInt().toByte() else buffer.readByte()
+
+    public fun readRoot(): Pair<String, NbtCompound> {
+        val type = readTagType()
+        require(type == NBTType.COMPOUND) { "Expected Compound Tag (10), got $type" }
+        val name = readString()
+        val root = readCompound()
+        return name to root
+    }
+
+    private fun readCompound(): NbtCompound {
+        val map = mutableMapOf<String, NBTElement>()
+        while (true) {
+            val type = readTagType()
+            if (type == NBTType.END) break
+
+            val name = readString()
+            map[name] = readPayload(type)
+        }
+        return NbtCompound(map)
+    }
+
+    private fun readList(): NbtList {
+        val elementType = readTagType()
+        val size = if (variant.isNetwork) buffer.readVarInt() else readInt()
+        if (size <= 0) return NbtList(elementType, emptyList())
+        val list = mutableListOf<NBTElement>()
+        (0 until size).forEach { _ -> list.add(readPayload(elementType)) }
+        return NbtList(elementType, list)
+    }
+
+    private fun readPayload(type: Byte): NBTElement {
+        return when (type) {
+            NBTType.BYTE -> NbtByte(buffer.readByte())
+            NBTType.SHORT -> NbtShort(readShort())
+            NBTType.INT -> {
+                val value = if (variant.isNetwork) buffer.readVarInt().decodeZigZag() else readInt()
+                NbtInt(value)
+            }
+
+            NBTType.LONG -> NbtLong(readLong())
+            NBTType.FLOAT -> NbtFloat(readFloat())
+            NBTType.DOUBLE -> NbtDouble(readDouble())
+            NBTType.BYTE_ARRAY -> {
+                val len = if (variant.isNetwork) buffer.readVarInt() else readInt()
+                NbtByteArray(buffer.readBytes(len))
+            }
+
+            NBTType.STRING -> NbtString(readString())
+            NBTType.LIST -> readList()
+            NBTType.COMPOUND -> readCompound()
+            NBTType.INT_ARRAY -> {
+                val len = if (variant.isNetwork) buffer.readVarInt() else readInt()
+                val array = IntArray(len) { readInt() }
+                NbtIntArray(array)
+            }
+
+            NBTType.LONG_ARRAY -> {
+                val len = if (variant.isNetwork) buffer.readVarInt() else readInt()
+                val array = LongArray(len) { readLong() }
+                NbtLongArray(array)
+            }
+
+            else -> throw IllegalArgumentException("Unknown Tag type: $type")
+        }
+    }
+}

libmc-nbt/src/commonMain/kotlin/cn/rtast/libmc/nbt/nbt_tags.kt

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+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/4
+ */
+
+
+package cn.rtast.libmc.nbt
+
+public sealed interface NBTElement {
+    public val typeId: NBTTypeID
+}
+
+public data class NbtByte(val value: Byte) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.BYTE
+}
+
+public data class NbtShort(val value: Short) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.SHORT
+}
+
+public data class NbtInt(val value: Int) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.INT
+}
+
+public data class NbtLong(val value: Long) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.LONG
+}
+
+public data class NbtFloat(val value: Float) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.FLOAT
+}
+
+public data class NbtDouble(val value: Double) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.DOUBLE
+}
+
+public data class NbtByteArray(val value: ByteArray) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.BYTE_ARRAY
+    override fun equals(other: Any?): Boolean = other is NbtByteArray && value.contentEquals(other.value)
+    override fun hashCode(): Int = value.contentHashCode()
+}
+
+public data class NbtString(val value: String) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.STRING
+}
+
+public data class NbtList(val elementType: Byte, val elements: List<NBTElement>) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.LIST
+}
+
+public data class NbtCompound(val map: Map<String, NBTElement>) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.COMPOUND
+}
+
+public data class NbtIntArray(val value: IntArray) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.INT_ARRAY
+    override fun equals(other: Any?): Boolean = other is NbtIntArray && value.contentEquals(other.value)
+    override fun hashCode(): Int = value.contentHashCode()
+}
+
+public data class NbtLongArray(val value: LongArray) : NBTElement {
+    override val typeId: NBTTypeID = NBTType.LONG_ARRAY
+    override fun equals(other: Any?): Boolean = other is NbtLongArray && value.contentEquals(other.value)
+    override fun hashCode(): Int = value.contentHashCode()
+}

libmc-nbt/src/commonMain/kotlin/cn/rtast/libmc/nbt/nbt_type.kt

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+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/4
+ */
+
+
+package cn.rtast.libmc.nbt
+
+public typealias NBTTypeID = Byte
+
+public object NBTType {
+    public const val END: NBTTypeID = 0
+    public const val BYTE: NBTTypeID = 1
+    public const val SHORT: NBTTypeID = 2
+    public const val INT: NBTTypeID = 3
+    public const val LONG: NBTTypeID = 4
+    public const val FLOAT: NBTTypeID = 5
+    public const val DOUBLE: NBTTypeID = 6
+    public const val BYTE_ARRAY: NBTTypeID = 7
+    public const val STRING: NBTTypeID = 8
+    public const val LIST: NBTTypeID = 9
+    public const val COMPOUND: NBTTypeID = 10
+    public const val INT_ARRAY: NBTTypeID = 11
+    public const val LONG_ARRAY: NBTTypeID = 12
+}

libmc-nbt/src/commonMain/kotlin/cn/rtast/libmc/nbt/nbt_variant.kt

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+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/4
+ */
+
+
+package cn.rtast.libmc.nbt
+
+import cn.rtast.libmc.common.ByteOrder
+
+public enum class NbtVariant(
+    public val order: ByteOrder,
+    public val isNetwork: Boolean,
+) {
+    JAVA(ByteOrder.BIG_ENDIAN, isNetwork = false),
+    BEDROCK_DISK(ByteOrder.LITTLE_ENDIAN, isNetwork = false),
+    BEDROCK_NETWORK(ByteOrder.LITTLE_ENDIAN, isNetwork = true)
+}

libmc-nbt/src/commonMain/kotlin/cn/rtast/libmc/nbt/varint.kt

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+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/4
+ */
+
+
+package cn.rtast.libmc.nbt
+
+internal fun Int.decodeZigZag(): Int = (this ushr 1) xor -(this and 1)
+internal fun Int.encodeZigZag(): Int = (this shl 1) xor (this shr 31)

libmc-nbt/src/jvmTest/kotlin/test/TestNBTReader.kt

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+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/4
+ */
+
+
+package test
+
+import cn.rtast.libmc.common.wrap
+import cn.rtast.libmc.nbt.NbtReader
+import org.junit.Test
+import java.io.File
+
+class TestNBTReader {
+
+    private val javaNBTBuffer = File("src/commonTest/resources/level.dat").readBytes().wrap()
+
+    @Test
+    fun `test read java nbt`() {
+        val readRoot = NbtReader(javaNBTBuffer).readRoot()
+        println(readRoot)
+    }
+}